Techniques such as, for example, PON and WDM are conventionally used in optical communication. “PON” is an abbreviation for Passive Optical Network. “WDM” is an abbreviation for Wavelength Division Multiplexing. According to a known configuration, a center controls the respective light wavelengths of optical transmitting apparatuses (see, e.g., Stephan Pachnicke, Stephen Mayne, Benoit Quemeneur, Daniel Sayles, Hendrik Schwuchow, Jiannan Zhu, Adrian Wonfor, Philipp Marx, Mirko Lawin, Markus Fellhofer, Richard Turner, Philipp Neuber, Marco Dietrich, Mike Wale, Richard V. Penty, Ian White, and Joerg-Peter Elbers, “Field Demonstration of a Tunable WDM-PON System with Novel SFP+ Modules and Centralized Wavelength Control”, OFC 2015 M2A.6, March 2015). A VOA is known that controls the level of light output and the like by attenuating the light using a variable attenuation amount. “VOA” is an abbreviation for Variable Optical Attenuator.